doc: Fix typo in expect_not_in_set_count().
doc: Fix typo in expect_not_in_set_count().

jhrozek/cmocka,VladimirTyrin/cmocka,clibs/cmocka,Odie/cmocka,jamesmunns/CMocka,tyc/cmocka,dsch/cmocka,linuxmaniac/cmocka,nuumio/cmocka,jschmidlapp/cmocka,jschmidlapp/cmocka,aleksandr-vin/cmock,JonathonReinhart/cmocka,wingyplus/cmocka,aleksandr-vin/cmock,lsjostro/cmocka,Odie/cmocka,jamesmunns/CMocka,clibs/cmocka,dsch/cmocka,nuumio/cmocka,jhrozek/cmocka,JonathonReinhart/cmocka,chadversary/cmocka,chadversary/cmocka,linuxmaniac/cmocka,Odie/cmocka,wingyplus/cmocka,VladimirTyrin/cmocka,jhrozek/cmocka,nuumio/cmocka,tyc/cmocka,tyc/cmocka,lsjostro/cmocka,jschmidlapp/cmocka